This invention relates to a continuous bag forming method and an apparatus for continuously forming bag-shaped containers from an inflation tube (tubular plastic film).
Plastic containers for sealing various liquid substances, e.g., containers for blood transfusion, have been conventionally formed by blow molding, because such containers have to be deformable. However, in blow molding one container is discontinuously formed in units of one molding. This has the disadvantage of raising costs and of large spaces being required for transportation.
In view of these disadvantages, a recently used method has bag-shaped containers formed of inflation tubes formed in continuous tubes. In this method, an inflation tube is cut into tubes of a required length, and both end openings of each tube of a required length are heat-sealed into a bag-shaped container. Alternatively, an inflation tube is heat-sealed at required parts and is conveyed by a pair of rollers to a next step where the inflation tube is severed at the heat seals, shaped in accordance with use, punched and subjected to other treatments to complete the bag-shaped containers.
However, the former method is difficult to automate and mostly depends on manual labor and as a result, the productivity is low, and dispersion tends to occur in the seal positions and the seal finish. It is a problem that uniform products cannot be produced. In the latter method, an inflation tube is conveyed by a pair of rollers. During its conveyance, tensile strength acts on the inflation tube, elongation occurs in the inflation tube and parts of the inflation tube are softened by heating for forming heat-seals. Resultant deflections take place in severing positions, punching positions and shaping which will follow in the next step. One problem is that precisely uniform products cannot be produced.
In either of these methods, the heat sealing of an tubular film is conducted by pressing heating means in the form of a heater against both sides of the tubular film for melt-adhesion to each other. When both sides of the tubular film are held by the heating means and heat-melted to each other, the melt-adhered parts and parts of the tubular film neighboring the melt-adhered parts or peripheral parts of the tubular film are semi-molten. The molten parts of the tubular film stick to the heating means and elongate the tubular film when the heating means is removed from the tubular film, or cause the tubular film to zigzag on conveyance. This deflects severing positions and punching to be conducted in the following steps. One problem is that precisely uniform bag-shaped containers of high quality cannot be prepared.
In forming bag-shaped containers, e.g., bag-shaped containers for sealing transfusion blood, of a tubular film and which are prepared by heat-sealing a tubular film widthwise at longitudinally set intervals and then severing the tubular film at the heat seals into lay-flat bags with one end open and the other end sealed. As shown in FIG. 27, a plastic cylindrical port a is generally inserted into the open end 1a of a lay-flat bag 1 and is melted onto the bag as the spout of the contained liquid substance when used.
To automate the operation of inserting the port a as described above into the open end 1a of the plastic lay-flat bag 1 and melting the port a onto the bag 1, it is necessary to automatically separate and open the lay-flat open end 1a to admit the port a.
Conventionally, the lay-flat open end 1a is opened rectangularly by putting vacuum pads on the front and the back sides thereof and drawing the vacuum pads apart from each other, and then the port a is inserted into the thus separately-opened end.
This conventional means has the following problems of, for example, in the case that a bag blank is thick, the lay-flat open end cannot be easily separated and opened. Even in the case that the bag blank is thin, it is difficult to separate and open the lay-flat end when a width of the open end is small. The separation and opening position tends to deviate. Especially in the case where a port a is automatically fed into the separated and opened end, the vacuum pads, their accessories, etc. are in the way to the automation.
In inserting the port a into the separated and opened end 1a of the bag 1 and melting the same thereonto conventionally, as shown in FIG. 28, the outer periphery of the port a and the separated and opened end 1a of the bag 1 are concurrently heat-melted onto each other by heating means d, d each having a concavity b contouring to a half circumference of the port a, and flat portions c, c on both sides of a concavity b, which are to abut on the separated and opened end 1a of the bag 1.
However, such conventional melt-adhering means has the following problems. That is, due to a remarkable difference in heat capacity between the port a and the bag 1, melt-adhering conditions differ between the port a and the bag 1. Resultantly cracks and pin-holes take place, and wrinkles occur in the melt-adhered portion. Defective ratios rise as a result.